 Patients will be randomized, at a 1:1 ratio, into bevacizumab plus erlotinib group or erlotinib alone group. Compute tomography CT or MRI scans will be performed every 6 weeks in the first 12 months since start of investigational drugs, and then performed every 12 weeks. Patients will be followed until documented progression at brain andor extra-cranial lesions. Patients with intracranial progression only are allowed to continue investigational drugs until a second progression of either intracranial progression or extracranial progression, developed, and the time-to extracranial progression will be determined. In patients with EGFR mutant advanced NSCLC who had brain metastases, it was reported that PFS to erlotinib or gefitinib was 6.6 monthsPark et al., 2012. In the current study, it is assumed that the median PFS, both intracranial and extracranial included, is 7 months for erlotinib group alone and is 12.3 months for bevacizumab plus erlotinib group hazard ratio 0.57 Seto et al., 2014. 109 patients will be required for analysis in this randomized phase II study. Patients will be stratified according to the EGFR L858R mutation and the EGFR exon 19 deletion mutation. 